I understand your concern for wanting to winterize your water softener. While you are waiting for an expert answer, I did manage to find a useful link that provides a lot of useful information about water softener. I hope my link is useful.

I am sending you an image from the owners manual with instructions for winterizing the water softener.

The owners manual has good information for maintaining and repairing the water softener. You can download, print, or view the owners manual free at [managemylife.com]. You need to enter the model number of the softener in the search field to access the owners manual.